As electronic devices become smaller, lighter, thinner, and more portable with the development of the information and communication industry, there is a growing demand for increasing the energy density of batteries used as a power source for such electronic devices.
A lithium battery, particularly, a lithium ion battery (LIB) is the battery which can best satisfy the above demand, and has been employed as a power source for various portable devices due to high energy density and simple design.
Recently, as use of lithium secondary batteries has been expanding from conventional small-sized electronic devices to large-sized electronic devices, automobiles, smart grids, and the like, a lithium secondary battery capable of maintaining excellent performance not only at room temperature but also even in harsher environments such as high or low temperature environments is required.
A lithium ion secondary battery is composed of a negative electrode made of a carbon-based material which can occlude and release lithium ions, a positive electrode made of a lithium-containing transition metal oxide, and a non-aqueous electrolyte. In a lithium ion secondary battery, lithium ions eluted from a positive electrode active material are intercalated into a negative electrode active material such as a carbon particle through 1st charging and the lithium ions are deintercalated through discharging. As lithium ions reciprocate between opposite electrodes as such, they transfer energy. Therefore, a secondary battery can be charged and discharged.
However, as the charging and discharging of a lithium ion secondary battery proceed, the structure of a positive electrode active material is destroyed, and thus performance of a positive electrode is degraded. Also, when the structure of a positive electrode is destroyed, metal ions eluted from a surface of the positive electrode are electrodeposited on a negative electrode, and thus the negative electrode is deteriorated. Such a deterioration of battery performance tends to be further accelerated when the potential of a positive electrode increases or a battery is exposed to high temperature.
Accordingly, there is a need to develop a positive electrode, an electrolyte, or the like having novel components which can solve the above problems.